1. Field of the Invention
The present invention relates to a method of removing the antimony from an antimony-containing copper electrolyte.
2. The Prior Art
During the electrolytic refining of copper, some of the impurities contained in the anode dissolve into the electrolyte, which is mainly an aqueous solution of copper sulfate and sulfuric acid, and accumulate in the form of metal ions. These impurities typically include nickel, antimony, arsenic, and bismuth. Since these impurities are liable to electrodeposition, the practice of measuring the concentrations of these impurities in the electrolyte and refining the electrolyte so as to keep their concentrations constantly below the prescribed levels proves to be very important to achieve the desired quality of copper electrodeposit.
More particularly, about 30 to 70% of all the antimony initially contained in the anode will dissolve out of the anode into the electrolyte, while the remainder will go into the anode slime. The concentration of antimony, which has a solubility of about 1.0 to 1.5 g/lit. in an ordinary copper electrolyte (Cu.sup.2+ ion concentration 40 to 50 g/lit., free sulfuric acid concentration 180 to 200 g/lit., and solution temperature 50.degree. to 60.degree. C.), will gradually increase in the electrolyte as the electrolysis proceeds. In electrolytic plants the antimony concentration is generally controlled to a range between about 0.3 and 0.6 g/lit.
Methods heretofore known for the separation of antimony from such copper electrolytes include an electrolysis method wherein the antimony is removed from the copper electrolyte in the form of a copper-removing electrolysis slime by using an insoluble anode (e.g. made of lead); a neutralization method wherein the antimony is removed in the form of a hydroxide by being hydrolyzed in the presence of sodium carbonate, for example, added thereto in advance; and a precipitation method wherein the antimony is removed in the form of a precipitated sulfide by blowing hydrogen sulfide gas into the electrolyte. These methods are for example described in the book Copper, The Science and Technology of the Metal, Its Alloys and Compounds, published by Reinhold Publishing Corp. (1954), the Journal of the Mining and Metallurgical Institute of Japan, Volume 97, No. 1122, and the Handbook of Metallurgical Technique, published by Asakura Shoten Co. Ltd. (1963). However, these methods invariably remove the antimony in conjunction with copper, arsenic, bismuth, etc. The slime obtained by any of these methods must be repeatedly treated in a preceding copper smelting process to recover the copper therein. Consequently, the greater part of the antimony is volatilized, contained into the flue dust, and piled up in most cases. Thus, the recovery of antimony in the slime has proved to be complicated, time-consuming, and very poor in separation efficiency. In addition, the antimony in the electrolyte will react with arsenic and bismuth contained in the solution to produce a white precipitate which is deposited in the form of scale on the heat transfer surfaces in the concentration facilities and on the inner surfaces of the circulating pipes. This scale is the main cause for operating troubles in such facilities and pipes.
To overcome the noted deficiencies in the prior art methods, the present inventors made a diligent study to find a method capable of providing a quick, efficient and easy separation of antimony from an antimony-containing copper electrolyte. The present invention resulted from this effort.